"Restenosis" refers to the renewed narrowing of an artery, e.g. a coronary artery, following a vessel opening or widening procedure, such as angioplasty or atherectomy. In restenosis, a vessel that has been treated to at least minimize the volume of a lesion or blockage and thereby restore blood flow, e.g. by balloon angioplasty, starts to renarrow, typically within about six months of the vessel widening procedure. This renarrowing often requires additional treatment, such as additional angioplasty procedures. It has been estimated that as much as one third to one half of all angioplasty procedures are followed by restenosis within the first six months to one year following the initial vessel widening procedure.
The cause of restenosis, and therefore identification of ways to prevent it, is the subject of intense interest. While it is known that restenosis is not caused by blood clots forming at the widened site, the cause of restenosis is not completely understood. One theory holds that restenosis is the cause of smooth muscle overgrowth of the vessel wall, perhaps as a result of the presence of large amounts of oxidants. Another theory holds that smooth muscle growth is not the primary cause of restenosis. Instead, restenosis results from scarring, which results in a remodeling and narrowing of the vessel.
A number of different protocols have been developed and/or are currently being investigated to treat and/or prevent restenosis. For example, antioxidant drugs such as probucol (Lorelco.TM.) have been employed with some success. Other smooth muscle cell proliferation inhibitors that have been tested for their ability to inhibit restenosis include calcium channel blockers, e.g. verapamil, and proteins such as angiopeptin. Another potential technique for preventing restenosis that is currently being clinically evaluated involves the use of radiation, where the surface of the treated vessel is exposed to radiation, e.g. via the use of .beta.-emitters. See e.g. the Beta-Cath.TM. System commercialized by Novoste Corporation and described at www.novoste.com. Yet other methods involve the use of stents to mechanically maintain the open vessel.
While a variety of different protocols are currently being tested for their effectiveness and safety in the prevention of restenosis (some of which have been described above), no particular technique has yet emerged as completely satisfactory. As such, there is continued interest in the development of new methods for preventing restenosis.